Thanks to flydream for sending details of Ghost Castles, a new ZX arcade game from Weird Science Software (who don't appear to be listed in Demotopia, oddly). What makes this game a little bit special is that it's available in an extended ROM version, with extra levels and stuff. Going by the guestbook on the WSS page it's had some good responses, so may well be worth at least downloading, or even paying for one of the release packages available (you can get it on Cassette or ROM, with optional G-Tech joystick interface).
Worth a look. Go on.